Most engines used for automobiles and the like include a number of belt driven accessory systems which are necessary for the proper operation of the vehicle. The accessory systems may include an alternator, air conditioner compressor and a power steering pump.
The accessory systems are generally mounted on a front surface of the engine. Each accessory has a pulley mounted on a shaft for receiving power from some form of belt drive. In early systems, each accessory was driven by a separate belt that ran between the accessory and the crankshaft. Due to improvements in belt technology, single serpentine belts are now generally used in most applications. A single serpentine belt routed among the various accessory components drives the accessories. The engine crankshaft drives the serpentine belt.
Since the serpentine belt must be routed to all accessories, it has generally become longer than its predecessors. To operate properly, the belt is installed with a pre-determined tension. As it operates, it stretches slightly over its length. This results in a decrease in belt tension, which may cause the belt to slip. Consequently, a belt tensioner is used to maintain the proper belt tension as the belt stretches during use.
A current trend of automobile manufacturers is to replace the traditional starting motor and generator with a single reversible starter-generator, which is connected to the crankshaft by means of a drive belt. During the start step, the starter-generator functions as a motor and drives the crankshaft of the internal-combustion engine; when the vehicle is in motion, instead, the starter-generator is driven by the internal-combustion engine and generates electric current for recharging the battery and running the auxiliary systems.
In the case where a starter-generator is used, the belt spans will have differing tensions according to the mode of operation. The span that is tight during the starting phase, in which the starter-generator is the driving member and the internal-combustion engine is the driven member, becomes slack in the stage of normal running, in which the internal-combustion engine is the driving member and the starter-generator is the driven member.
To overcome this problem bi-directional belt tensioners or two-arm belt tensioners, i.e., which comprise two arms provided with pulleys, each acting on a respective span of the belt are known. The two arms can be mounted on the same pivot point in order to pivot about a common axis. The arms are loaded in the direction of one another by a spring so that the respective pulleys will co-operate with respective spans of the belt, thereby ensuring their proper tension.
Representative of the art is US 2002/0039944 which discloses an improved belt tensioner for a belt drive system having a belt tensioner, a crankshaft pulley, an accessory pulley, and a motor/generator pulley. The belt drive system further includes a power transmission belt trained about the crankshaft pulley, the accessory pulley, and the motor/generator pulley. The belt tensioner is of the type including an attachment point adapted to be affixed to a stationary point relative to a cylinder block of an engine, a first belt tensioner pulley, a biasing member, and a connective portion adapted to communicate a force from the biasing member to the power transmission belt via the first belt tensioner pulley. It is improved by the belt tensioner including a second tensioner pulley, and the connective portion being adapted to communicate the force from the biasing member to the first tensioner pulley and to the second tensioner pulley and thereby mutually asymmetrically biasing the first tensioner pulley and the second tensioner pulley toward movement tending to increase tension upon the power transmission belt.
What is needed is a tensioner having a pivot shaft having two facing frustoconical portions disposed on a common axis, each of the first pivot arm and second pivot engaged with a respective facing frustoconical portion. The present invention meets this need.